1. Field of the Invention
The invention relates to an optoelectronic sensor, especially a reflection photoelectric barrier or a reflection light sensing device, for detection of an object in a monitored area, with a housing, with transmitting and receiving optics and with an evaluation circuit. In addition, the invention relates to a process for detection of an object in a monitored area, with an optoelectronic sensor, an electrical transmitted signal being converted into an optical transmitted signal, the optical transmitted signal being emitted into the monitored area, reflected back as the optical received signal at least in part to the optoelectronic sensor by a reflector or an object, and being converted into an electrical received signal.
2. Description of Related Art
Known optoelectronic sensors always have an opto-transmitter and at least one opto-receiver. Here, the transmitting components, therefore the light-emitting components, are typically diodes, preferably laser diodes, and the receiving components are generally photodiodes. Optoelectronic sensors can be divided essentially into three different types, specifically one-way systems, reflection systems and sensor systems.
One-way systems consist, on the one hand, of a transmitter device, and on the other hand, of a receiver device which is separated from it in space. The transmitter device and the receiver device are located opposite one another on the lateral boundaries of an area which is to be monitored so that the light emitted by the transmitter device can be received by the receiver device. The disadvantage here is that two electronic devices must be required, mounted and supplied with electrical energy. In contrast, in reflection systems, which are also called reflection photoelectric barriers, transmitters and receivers are integrated in a single unit, therefore in a single device.
Such a unit, which constitutes a transmitter/receiver device, is located on the outer boundary of the area which is to be monitored, while on the other boundary of the area which is to be monitored, which latter boundary is opposite the former boundary, a reflector, for example, a triple mirror, is provided which reflects the light emitted by the transmitter/receiver device back onto the latter such that it can be received by the receiver which is integrated in the transmitter/receiver device. Compared to the one-way system, the reflection photoelectric barrier offers the advantage that only one electrical connection is necessary and the reflector by virtue of its special property need only be relatively roughly aligned to the reflection photoelectric barrier.
Reflection photoelectric barriers can be divided into two groups based on their optical structure. In so-called genuine autocollimation systems, separation of the transmitted and received beam is done with a semitransparent mirror or a polarization filter. In the second group of reflection photoelectric barriers, geometrical division of the transmitted and received beam is done by transmission optics and separate receiving optics which is arranged offset to it. The opto-transmitter and opto-receiver are located almost parallel, but at a short distance from one another, in the housing. This reflection photoelectric barrier with transmission optics and second receiving optics is known, for example, from published German Patent Application DE 42 38 116 C2.
It is common to the two above described systems—the one-way system and the reflection system—that the receiver does not receive a light signal or only receives a reduced light signal when there is an object in the area which is to be monitored, since this object completely or at least partially interrupts the beam path of the light which has been emitted by the transmitter. The opto-receiver thus normally—no interruption of the monitored section—detects the light beam which has been emitted by the opto-receiver, and the emitted light pulses.
Basically, different from this manner of operation is the manner of operation of optoelectronic sensing device systems, also called reflection light sensing devices. In these systems, the transmitter and the receiver are likewise located together in a unit. However, in contrast to the reflection photoelectric barrier, there is no reflector as a component of the system. Instead, the light emitted by the transmitter in the transmitter/receiver device is reflected on an object which is to be detected. If at least part of the light which has been reflected by an object is reflected onto the transmitter/receiver device, this reflected portion of light can be detected by the receiver. Reflection light sensing devices are known, for example, from German Patent DE 35 13 671 C3 (and corresponding U.S. Pat. No. 4,782,224), and published German Patent Applications DE 43 11 691 A1 and DE 199 33 439 C2.
As a result of the generally more poorly reflecting surface of the object compared to a reflector, reflection light sensing devices have a shorter range than reflection photoelectric barriers. However, reflection light sensing devices have the advantage that they do not require a second active element like one-way photoelectric barriers and do not require a reflector like reflection photoelectric barriers. Reflection light sensing devices for proximity optoelectronic detection of articles work either as energy V-light sensing devices or as light sensing devices using the triangulation principle.
In an energy V-light sensing device, the emitted light is diffusely reflected on the object which is to be detected. Some of the reflected light is incident on the opto-receiver and initiates a switching process. The two states—reflection or lack of reflection—are evaluated; they are equivalent to the presence or absence of articles in the sensing area. As dictated by the system, the sensing range of the single energy V-light sensing device is therefore highly dependent on the degree of reflection of the object which is to be monitored. The opto-transmitter and opto-receiver can therefore have common transmitting/receiving optics, downstream of the transmitted/receiving optics there being a beam splitter which deflects the light which has been reflected by the object to the receiver.
Triangulation light sensing devices work according to the double lens principle, i.e., the transmitting optics and the receiving optics are separated from one another in space and the transmitted beam and the received beam form an angle to one another. The intersection point of the transmitted beam and the received beam determines the maximum sensing distance of these systems. Due to the relatively minor technical complexity, triangulation light sensing devices using two photodiodes—one for the near area and one for the remote area—are commonly used. The operating distance is determined by the lateral position of the separating line between the two photodiodes.